MEMS Pressure Sensor Vacuum Cavity Trench Isolation
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Solution Overview
Problem
Micro-electro-mechanical pressure sensors using semiconductor materials face sensitivity issues due to temperature variations causing spurious pressure from trapped gases in buried cavities, leading to reading errors and offset compensation challenges.
Innovation Solution
The design incorporates a pressure sensor with a membrane suspended in a vacuum environment, using air gaps and a trench structure to isolate the sensitive portion from the supporting portion, and employs a getter region to trap residual gases during bonding, ensuring the membrane is exposed to external pressure without trapped gas interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the membrane is formed by epitaxial growth in a deoxidising environment above the buried cavity, then the membrane can be successfully formed, but gas (hydrogen) remains trapped within the buried cavity causing spurious pressure and reading errors
Solution Approach 1:
The patent extracts the harmful trapped gas from the buried cavity by forming a through-trench that connects the cavity to the external environment, allowing the gas to escape and eliminating the source of spurious pressure that causes reading errors
Solution Approach 2:
The patent introduces a getter material as an intermediary substance within the buried cavity that actively absorbs residual gases, preventing them from exerting spurious pressure on the membrane while maintaining the structural integrity of the device
2Ease of manufacture
If the buried cavity is sealed during manufacturing, then the structure is complete, but temperature variations cause gas expansion/contraction generating spurious pressure against the membrane
Solution Approach 1:
The patent removes the problematic sealed buried cavity configuration by forming a through-trench that opens the cavity to the external environment, eliminating the trapped gas that expands and contracts with temperature changes
Solution Approach 2:
The patent changes the physical state of the cavity from sealed to open by creating a through-trench, fundamentally altering how pressure is managed within the cavity and eliminating temperature-dependent spurious pressure generation
3Strength
If the sensitive portion is connected to the peripheral portion, then the structure is mechanically stable, but packaging stress is transferred to the sensitive portion causing measurement errors
Solution Approach 1:
The patent segments the device into a suspended sensitive portion and a peripheral portion by forming a trench that separates them, allowing the sensitive portion to be mechanically isolated from packaging stress while maintaining structural integrity
Solution Approach 2:
The patent introduces elastic elements (springs) as intermediary components that connect the suspended sensitive portion to the peripheral portion, providing mechanical support while isolating the sensitive portion from packaging stress through the compliant spring elements
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces reading errors, improves pressure detection linearity, simplifies signal processing, and reduces testing time by maintaining a vacuum environment around the membrane, enhancing sensitivity and accuracy.
Implementation Method 1
The design incorporates a pressure sensor with a membrane suspended in a vacuum environment
Implementation Method 2
employs a getter region to trap residual gases during bonding
Data Source
Figure 1~4
Figure 5A~10B
Figure 11~17
AI summary
A micro-electro-mechanical pressure sensor device (100), formed by a cap region (102) and by a sensor region (101) of semiconductor material. An air gap (107) extends between the sensor region (101) and the cap region (102; 103); a buried cavity (109) extends underneath the air gap, in the sensor region (101), and delimits a membrane (111) at the bottom. A through trench (110) extends within the sensor region (101) and laterally delimits a sensitive portion (121) housing the membrane, a supporting portion (120), and a spring portion (122), the spring portion connecting the sensitive portion (121) to the supporting portion (120). A channel (123) extends within the spring portion (122) and connects the buried cavity (109) to a face (101A) of the second region (101). The first air gap (107) is fluidically connected to the outside of the device, and the buried cavity (109) is isolated from the outside via a sealing region (106B) arranged between the sensor region (101) and the cap region (102).